This invention relates to optical apparatus, and in particular to a reflective optical apparatus that interconverts between a point of light and a line of light.
In optical systems such as linear displays and scanners, it is sometimes necessary to interconvert a light beam between a point of light and a line of light. xe2x80x9cPointxe2x80x9d and xe2x80x9clinexe2x80x9d are used in the sense of ideally being non-dimensional and one-dimensional features, respectively, but in reality having some breadth in other dimensions. For example, it may be necessary to produce a line of light for scanning or other output purposes from a point light source such as an optical fiber, a light emitting diode (LED), a laser diode, or a point external input to the optical system. In another example, it may be necessary to produce a point of light for analysis or other output purposes from a linear light source such as a linear filament or a linear external input to the optical system.
The available optical devices for making such a point-line interconversion utilize multiple lenses, usually at least a cylindrical lens and usually also a spherical lens. In a typical case, such optical devices include four lenses, some of which are cylindrical lenses and some of which are spherical lenses. These available interconversion devices have several drawbacks. Such multiple-lens systems are heavy, occupy a large volume and length in the beam path, are expensive, and are prone to misalignment. Additionally, lenses are prone to introduce aberrations into the beam passing therethrough, in the form of monochromatic and/or polychromatic aberrations. As a result, the desired interconversion between the mathematical line of light and the mathematical point of light is not as sharp as might be desired. Intrinsic aberrations (chromatic and monochromatic) and fabrication and alignment errors all contribute to the quality or fineness of the imaged point or line of light.
There is a need for an improved approach to the interconversion between a line of light and a point of light. The present invention fulfills this need, and further provides related advantages.
The present invention provides an optical apparatus for interconverting a light beam between a point of light and a line of light. The present approach uses no refractive lenses, reducing the problems associated with refractive optical systems such as excessive weight and size, expense, and misalignment. Significantly, the present approach does not introduce aberrations into the light beam, so that the interconversion between the point of light and the line of light is sharp and precisely defined, and is limited only by the diffraction of light. The present approach uses only a reflective optical element, so that the line/point interconversion optical system may be made light in weight, compact, inexpensive, resistant to misalignment, and free of monochromatic and polychromatic aberrations.
In accordance with the invention, an optical apparatus comprises a nonplanar light-reflecting surface having a shape referenced relative to an orthogonal axial system having an x-axis, a y-axis, and a z-axis. The light-reflecting surface has a non-circular conic profile with a conic axis and a distance f from a conic vertex to a finite focal point of the conic, wherein the non-circular conic profile is determined in a yz-plane containing the y-axis and the z-axis. The non-circular conic profile may be, for example, an ellipse, a concave or convex hyperbola, or, most preferably, an off-axis parabola. The light-reflecting surface further has a circular profile with a circular center and a radius of curvature r numerically equal to the distance f from the conic vertex to the finite focal point of the conic, wherein the circular profile is determined in an xz-plane containing the x-axis and the z-axis.
The optical apparatus further optionally includes a point light transceiver at a transceiver location. The transceiver location lies on the conic axis in the yz plane at the finite focal point a distance f away from the conic vertex, and also at the circular center in the xz plane. The point light transceiver may be a point light source directing a light beam toward the reflecting surface, at a single-wavelength or at multiple-wavelengths. The point light transceiver may instead be a point light receiver receiving a light beam from the reflecting surface. The light-reflecting surface may be concave or convex relative to the point light transceiver.
More generally, an optical apparatus effects an interconversion of a light beam between a non-dimensional point at a first location and a one-dimensional line at a second location. The optical apparatus comprises a nonplanar light-reflecting surface positioned on a beam path between the first location and the second location. The light-reflecting surface has a compound curvature having a non-circular conic profile with a conic axis and distance f from a conic vertex to a finite focal point of the conic, wherein the non-circular conic profile is determined in a first reference plane, and a circular profile with a circular center and a radius of curvature r numerically equal to the distance f from the conic vertex to the finite focal point of the conic, wherein the circular profile is determined in a second reference plane orthogonal to the first reference plane. Either a light source or a light receiver may be placed at either the first location or the second location. The optical apparatus preferably has exactly one nonplanar light-reflecting surface between the first location and the second location.
The present approach utilizes a compoundly curved reflecting surface (i.e., a mirror) to interconvert between the line of light and the point of light. Because the reflecting surface acts in a reciprocal manner on light traveling in opposite directions along the beam path, the interconversion may be between a light introduced as a line and output as a point, or light introduced at a point and output as a line. Thus, a point source may be used to produce a line output, or a line source may be used to produce a point output. xe2x80x9cPointxe2x80x9d and xe2x80x9clinexe2x80x9d are used herein to refer to features that are non-dimensional and one-dimensional, respectively, in their mathematical idealizations. In practice, however, there is always some diffraction into one or two dimensions for a point, or into two dimensions for a line. This spreading beyond the idealization results in some spreading of the interconverted form, but this effect does not negate the applicability of the present invention.
Desirably, the optical apparatus has no refractive optical element such as a lens therein. That is, it is preferred that the optical apparatus is reflective only, in accomplishing the interconversion between a point of light and a line of light. The optical apparatus may be used in applications with other optical components, which may include refractive optical components. But the refractive optical components are preferably not part of the point/line interconversion optical apparatus.
The use of reflective optics to accomplish the point/line light interconversion, preferably in the form of a single curved reflecting surface, has important advantages. The optical apparatus is light, compact, and inexpensive to manufacture, inasmuch as the single reflecting surface may be made of coated plastics or other materials that are light in weight, and only one optical element is used. The reflecting surface may be readily manufactured by injection molding of a plastic material, or diamond-point turning of aluminum or other material. Because only one optical element is used, the optical apparatus is more resistant than a refractive optical system to the introduction of internal misalignments in assembly and/or in service. There is no internal misalignment of the optical elements, because there is only the one reflecting surface in the preferred approach, although there may be misalignment of the light source and the reflecting surface. The reflecting surface used in the optical apparatus functions independently of the wavelength of the light beam being reflected, so that there is no polychromatic aberration introduced into the light beam, regardless of the single wavelength or multiple wavelengths of the light beam. Because the reflecting surface is a conic, there are no monochromatic aberration in the interconversion between the point of light and the line of light.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.